Contact for interrupter switch



D'ec. 16, 1958 H. c. GRAVES, JR 2,864,921

CONTACT FOR INTERRUPTER SWITCH Filed July 28. 1955 24 ENLA/QGEO v/sw 1 32 y E- 4 E5: 5-

IN VEN TOR. 52mm 7 6'. 664 v5.9, Je.

BY W

United States Patent CONTACT FOR INTERRUPTER SWITCH Herbert C. Graves, Jr., Pittsburgh, Pa., assignor to Gibson Electric Company, Pittsburgh, Pa., a corporation of Pennsylvania Application July 28, 1955, Serial No. 524,977

3 Claims. (Cl. 200-166) tinguishing the are formed during the opening or separation of arcing contacts under load conditions. The details of operation of this type of device are sufficiently described in either of the above mentioned patents and need not be referred to in detail here.

It is sufficient to say that such an interrupter involves the rapid axial movement of a plunger rod which has rigidly secured thereto, an insulating portion of organic material of such a nature that upon being heated to the decomposition state it evolves large percentages of hydrogen and carbon monoxide, which tend to extinguish any are which is formed when the circuit is broken.

At the time the contacts are opened, an arc is drawn between the electrical contacts, which comprise a refractory material and a conductive metal, such as silver. One of these contacts is in the form of a ring which is inserted between the conductive and non-conductive portions of the plunger rod. conventionally, this ring is merely an annular segment composed of refractory material and a conductive metal. The surfaces of the said ring are flat. It has been found, through repeated use, that these surfaces become oxidized and are subject to abnormal heating and therefore split the contact ring.

Moreover, the contact between a silver-refractory material surface, such as silver-tungsten, and the copper surface of the rod results in a joint having a high millivolt drop. This causes instantaneous increases in heat at the contact surface in addition to the arcing surface, thereby increasing the tendency of such rings to split and otherwise deteriorate. I have found that by providing, in a plunger type interrupter switch, a novel contact comprising an, annular ring having one'surfacethereof serrated and having the serrations at least partially filled with conductive material, such as silver, that these disadvantages can be overcome.

Moreover, by coating such acontact surface with silver the millivolt drop between the surface of the contact and the conductive or copper portion of the plunger rod, is substantially reduced thereby resulting in a more efficient switching operation, and the contacts used maintain their original quality and have a longer life.

Accordingly, it is an object of my invention to provide a novel serrated type electrical contact particularly suitable for use in connection with plunger type interrupter switches.

It is another object of my invention to provide, in combination, an interrupter switch having clamped thereto an annular serrated contact which may be clamped against the portion of the plunger rod which has a con- 'sintering and impregnating with silver. may be formed either in the pill pressing operation or by ductive surface and thereby reduce thermal shock and the susceptibility to fracture, which has been inherent in contacts of the prior art.

These and other objects of my invention will become more apparent when taken in connection with the following description and the drawings in which:

Figure 1 shows in cross-section a plunger type interrupter switch for which my novel contact is particularly adapted.

Figure 2 illustrates, in magnification, the annular type contact which is the subject of my invention.

Figure 3 is a cross-sectional view taken along the lines 3-3 of Figure 2 and looking in the direction of the arrows.

Figure 4 is a magnification of the serrated surface of the contact as it appears in Figure 3.

Figure 5 is a magnified view of how the serrated surface of the contacts would be in engagement with a metallic surface such as the plunger rod shown in Figure 1.

Essentially my invention involves a novel serrated type electrical contact which is annular in shape and has a surface perpendicular to the axis thereof serrated. These serrations are then at least partially filled with conducting material such as silver and are at the same time coated with a thin layer of pure silver. The contact material comprises a conductive and a refractory metal and preferably a silver-tungsten composition.

This annular element is then inserted in between the conducting portion of the plunger rod which is usually copper and the non-conducting extension thereof which is usually a horn, nylon or bone fibre or other organic material which decompose to liberate hydrogen, carbon mooxide and a small percent of hydrocarbon, thereby effectively extinguishing any are which is drawn upon the separation of the contacts.

The serrations on the surface of my novel contact may take various forms, but preferably are in the shape of isolated circular concentric rings. Basically the contact is formed by conventional procedures and is well known to the art. Such procedures include the mixing of silver or other conducting metal with a refractory metal powder generally from the group consisting of tungsten, tungsten carbide, molybdenum, molybdenum carbide and mixtures thereof, pressing them to form a porous metal and then The serrations a coining process. Details and relative advantages of these methods can be found in my Patent No. 2,641,670 and need not be repeated here as they form no part of the present invention, and are now well known to the art.

Referring now to Figure l, plunger rod 10 comprises a metallic conducting portion 11 which is usually made of copper and an extension or follower 12 therefor, which is made of a horn, nylon or bone fibre' or other organic materials, which when an arc is struck will give off hydrogen and carbon monoxide as previously mentioned and thereby will aid in the rapid extinguishing of such an arc. The plunger assembly rides in a bone fibre tube (not shown). Spring or other means 14 is provided so that the plunger may be readily and rapidly moved in an axial direction. Figure 1 illustrates the normally closed position of the switch in which spring loaded contacts 18 are in direct engagement with the copper portion of the rod 11.

As the plunger is pulled downwardly in a direction indicated as A the relative position of the spring loaded contacts will be that shown by the dotted lines 18a in which case they will contact the bone fibre thereby resulting in an open circuit. The point at which the circuit makes or breaks occurs when the annular contact element 20 meets the contact element in the spring loaded contact 18. It is these contact elements 18 to which my invention particularly refers.

Before discussing them in more detail it should be noted that the copper rod is joined to the non-conductive follower having one end of the copper rod 25 machined to a smaller diameter and then threaded as indicated at 26. The organic insulating material is then screwed on or otherwise attached to the threaded portion of the copper rod.

Figures 2 and 3 show contact element 20 in more detail and indicate the concentric serrations thereon.

In Figures 4 and 5 it can be seen that these serrations are filled with a conducting metal which is usually silver, 28. As stated these serrations take the form of circular concentric rings and the surface of such serrations 32 are coated with a thin layer of pure silver. Additional pure silver is placed, during the impregnating process, in the cavities or valleys between serrations. Specifically the amount of excess silver is so controlled that in no case does it so completely fill the space between serrations as to cause a projection of pure silver above a plane through the top of the serrations. The contacts are clamped rather than brazed or welded to the copper surface. Ordinarily the flat surfaced contacts of this type when clamped against copper might break and corrode and tend to split because of the high millivolt drop between the arcing ring and the copper to which it is clamped. This causes instantaneous increases in heat at the contact surface in addition to the arcing surface which causes the rings to split. The use of serrations plus a silver surface decreases this high millivolt drop at the clamped joint, thus the silver surface will maintain a relatively low temperature so as to prevent this thermal shock resulting from the high resistance at the clamped joint.

In order to further decrease the millivolt drop the surface of the copper plunger rod which is clamped to the contact may be silver surfaced.

One advantage of my contact is that it places a silver surface rather than a silver-tungsten surface against the copper surface. Of course, if the copper is silver plated, the two surfaces become silver to silver. Also, the sharp edges of the serrations of my contact dig into the copper surface and cause a relatively high concentration of the available clamping force at the joint between the silvertungsten contact and the copper rod.

This is, of course, a removable or replaceable type contact and makes for easy maintenance of the equipment of which the illustrated plunger forms a part. This type of assembly avoids the necessity for a brazed joint and thus the entire length of copper used in the plunger is maintained at its original hardness. Not only is the type of contact of my invention applicable for the arcing ring but it may be used as element 24 in the spring loaded contact. be at and allows for a relatively low millivolt drop between contact element 24 and the copper tulip section 18.

As I have stated any of the conventional contact com- In this case the serrated surface would positions may be used in my invention. These include tungsten, tungsten carbide, molybdenum, and molybdenum carbide infiltrated with silver. I prefer, however, to use as my contact composition one containing percent tungsten and 25 percent silver. When provided with the serrations and coated with silver, as I propose, such contact is not readily subject to fracture under the thermal shock which may be inherent in the operation of an interrupter switch of the type disclosed.

in the foregoing, I have described my invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of my invention within the scope of the description herein are obvious. Accordingly, I prefer to be bound not by the specific disclosure herein, but only by the appended claims I claim:

1. An interrupter switch comprising a copper rod having an extension of organic insulating material, means for imparting in reciprocal fashion an axial motion to the said conductive and non-conductive rod, contact means spring biased radially against the outer surface of the said rod and annular contact means positioned between the copper and insulating portions of the said rod, the said annular contact means comprising a pressed and sintered refractory material impregnated with silver and having a silver-coated serrated face, said face being clamped in contact with the copper portion of the rod thereby forming a silver-to-copper joint, the cavities between the serrations being partially filled with silver, the amount of said silver therein being limited so that it does not extend above the plane defined by the top of the said serrated surface.

2. The switch of claim 1 in which the conductive copper surface in contact with the annular contact is silver plated.

3. An interrupter switch comprising an electrically conductive rod having rigidly secured thereto an extension of organic insulating material, an annular serrated contact positioned between the said conductive and insulating portions of the rod, the serrations on the surface of said contact being silver-coated and clamped in contact with the conductive portion of the said rod, a contact spring loaded radially inward against the rod, the said spring loaded contact being provided with an annular contact member having one surface thereof silver-coated and serrated, the cavities between the serrations being at least partially filled with silver, the said serrated surface further being in contact with the metallic portion of the said spring loaded contacts.

References Cited in the file of this patent UNITED STATES PATENTS 2,118,355 Matthews May 24, 1938 2,490,020 Enzler Dec. 6, 1949 2,641,670 Graves June 9, 1953 2,646,486 Udale July 21, 1953 2,715,169 High Aug. 9, 1955 

1. AN INTERRUPTER SWITCH COMPRISING A COPPER ROD HAVING AN EXTENSION OF ORGANIC INSULATING MATERIAL, MEANS FOR IMPARTING IN RECIPROCAL FASHION AN AXIAL MOTION TO THE SAID CONDUCTIVE AND NON-CONDUCTIVE ROD, CONTACT MEANS SPRING BIASED RADIALLY AGAINST THE OUTER SURFACE OF THE SAID ROD AND ANNULAR CONTACT MEANS POSITIONED BETWEEN THE COOPER AND INSULTINMG PORTIONS OF THE SAID ROD, THE SAID ANNULAR CONTACT MEANSCPOMPRISING A PRESSED AND SINTERED REFRACTORY MATERIAL IPREGNATED WITH SILVER ANS HAVING A SILVER-COATED SERRATED FACE, SAID FACE BEING CLAMPED IN CONTACT EWITH THW COOPER PORTION OF THE ROD THEREBY FORMING A SILVER-TO COOPER JOINT, THE CAVITIES BE- 